The present invention generally relates to charged particle beam drawing apparatus for drawing by irradiating an electron beam or ion beam on a sample, and particularly to a charged particle beam drawing apparatus for drawing by using bitmapped pattern data during the raster scanning of a charged beam.
The charged particle beam drawing apparatus includes, for example, electron beam apparatus and focused-ion beam apparatus. These apparatus deflect the charged particle beam with high precision and irradiate it on the object being processed to thereby finely work upon the object. These apparatus are widely used chiefly for manufacturing semiconductor devices.
Here, an example will be mentioned of producing an integrated circuit pattern on a semiconductor sample by using an electron beam apparatus. The semiconductor sample is coated with a substance called resist that is sensitive to the electron beam. The electron beam apparatus irradiates the electron beam on the resist while referring to the designed integrated circuit pattern to draw the integrated circuit pattern on the resist. The raster scanning type electron beam apparatus deflects the shapely focused spot beam to make raster scanning, and controls the beam to turn on and off in accordance with the integrated circuit pattern, thus drawing.
In the raster scanning system, in order to control the spot beam to turn on and off, draw data (data representative of on and off) is generated from the integrated circuit pattern, and used to control the spot beam. In general, the draw data can be expressed by bitmapped image data.
The integrated circuit pattern is converted from the designed data (CAD format) to intermediate data suited to process by the drawing apparatus, and stored in a storage device. At the time of drawing, the intermediate data is converted to the bitmapped data. This process mentioned above is performed on a PC (personal computer) or WS (work station). If the designed data is tried to develop into bitmapped data by using WS or the like, vast amounts of processing time and huge volumes of data will be necessary.
As a prior art for converting from the designed data to the bitmapped data, there is a bitmapped data producing method to be used in the raster scanning type electron beam apparatus that is disclosed in, for example, JP-A-8-505003.
The conventional method will be described with reference to FIG. 2.
Referring to FIG. 2, an apparatus to carry out this method includes a computer 201 into which CAD format data is inputted, pre-processing means 202 for generating intermediate data from CAD data, bitmapped data generating means 203 for generating bitmapped data, a storage device 204 for storing the bitmapped data, and an optical system 205 for drawing by referring to the bitmapped data stored in the storage device. This method will be described with reference to, for example, the pattern shown in FIG. 3. A circuit layout pattern representative of a polygon is divided into partial figures such as oblong rectangles and trapezoids, and then processed. Since the pattern is the collection of simple figures as illustrated in FIG. 3, it is not divided, but oblong rectangles 302, 303 and a trapezoid 301 are defined as partial figure data. These figures are expressed by information of their type, start-point, end-point, length and angle. These intermediate data are converted to bitmapped image data. FIG. 4 is a magnified view of a region 304 shown in FIG. 3. A region 402 is a pixel. A technique such as DDA (Digital Differential Analyzer) is used to compute the intersections of figures and each raster, thus determining boundaries of figures in each raster. The figure in each raster is marked out according to the computed boundaries of figures. This operation is repeated for all rasters. FIG. 5 is a magnified view of a region 401 of 64 pixels shown in FIG. 4. The partial figure data is converted to bitmapped image data of binary values of on (1) and off (0) as shown in FIG. 5. The bitmapped partial figure data are sequentially stored in a high-speed memory that has two-dimensional addresses corresponding to the actually depictive region. In this case, the pieces of data written in the same address are logically summed so that figures are prevented from being overlapped. In this way, the bitmapped data are produced over the entire depicted regions.
The procedure for drawing is performed such that the image data of a depicted unit region is produced and then the bitmapped data are sequentially read according to the scanning direction to draw.
In the electron beam apparatus as described above, the intermediate data is previously produced and held in the storage device, and when drawing is made, the bitmapped data for the necessary region is generated with high speed. That region is drawn by referring to the produced bitmapped data.